WG 6 - TC 112/WG 6

IEC TS 61857-42:2025 provides a procedure to evaluate the lifetime of an electrical insulation system (EIS) in a drivetrain unit within road transportation (automotive) applications. Typical applications include motors and generators in hybrid and full electric passenger vehicles, light-duty and heavy-duty commercial vehicles, as well as buses.
In general, the IEC 61857 series is applicable to EIS used in electrotechnical products with an input voltage of up to 1 000 V where the predominant ageing factor is thermal. In the context of this document the limit of 1 000 V is understood to be the application-specific battery DC voltage.
The EIS evaluated by this procedure will operate free from partial discharges over its whole lifetime.
Evaluation of EIS in the following applications is outside the scope:
- motors and generators within the scope of IEC TC 2, Rotating machinery;
- rail traction machines in the scope of IEC TC 9, Electrical equipment and systems for railways;
- motors and generators for road vehicles that are not intended for the traction of them.

IEC TR 61857-2:2025 gives guidelines to identify the appropriate test method for the evaluation of a proposed electrical insulation system (EIS). Some of the standards evaluate the EIS using one stress factor which is thermal. Other standards evaluate the thermal stress factor with adjustments to the conditioning applied prior to the diagnostic testing to simulate applications in air. A third group of these standards when the application is other than in air. This technical report is applicable to existing or proposed EIS used in electrotechnical products across a wide range of operating voltages of IEC Standards. The report takes care to identify the appropriate standard based on construction and intended operating application.
For all performance and safety requirements related to an application, refer to the technical committee requirements for the application.
This edition includes the following significant technical changes with respect to the previous edition.
a) The Introduction is expanded to convey that both TC 112 and TC 2 have established EIS test standards.
b) Clause 4 introduces the fact that there are four stress factors, not only thermal. This essential concept carries over into part of Clause 5.
c) The large number of established standards are organized into common concept groups in Tables 1 to 5:
1) Table 1 covers an overview of EIS evaluations for background and structure.
2) Table 2 covers evaluation of test objects prior to the start of long-term thermal ageing using screening tests.
3) Table 3 covers test standards for the evaluation of thermal stresses in air and has an increased number of standards.
4) Table 4 covers standards for special environmental applications other than in air
5) Table 5 covers standards for the modification of an established EIS.

IEC 63177:2024 specifies the test method for the compatibility of construction materials with electrical insulating liquids for use in electrical equipment, such as liquid-immersed transformers and tap-changers, liquid-impregnated capacitors, and liquid-cooled rotating machines used in electrical vehicles and oil pumps. This document is applicable to mineral insulating liquids, natural esters, silicone insulating liquids, synthetic organic esters, modified esters, capacitor fluids based on synthetic aromatic hydrocarbons and e-transmission fluids used in electrical vehicles and oil pumps. The compatibility tests are not sufficient for a full qualification of construction materials for a given application without additional tests requested by the appropriate IEC Technical Committee or equipment manufacturers.

IEC TR 61858-3:2020(E) provides information on the identification of electrical insulating materials and auxiliary components for the assessment of modifications to an established insulation system and gives guidance on the selection of feasible test procedures.

IEC 61857-32:2019 series is focused on applications where other possible factors need to be incorporated to evaluate any influence on the performance of the electrical insulation system (EIS). Multi-factor evaluation is the most complex type of project to design and conduct. Clear guidelines are needed to give the user of this document a uniform approach and a method to analyse the test results.
This document is for applications where the stresses are some combination of other factors of influence identified in IEC 60505. The multi-factor stresses are applied during the diagnostic portion of each test cycle.
A few examples of other factors of influence or multi-factor stresses are:
– high vibration;
– submersion in oils, water, or solutions;
– voltage higher than the test voltage of the reference EIS;
– decreased cold shock temperature.

IEC 61857-31:2017 establishes an EIS evaluation for applications with a designed life of 5 000 h or less. This test method follows the procedures of IEC 60505 and is modified based on the range of designed life.

IEC TS 62332-3:2016 is applicable to EIM and EIS containing solid and liquid components where the refrigerant, oil and thermal stresses are the dominant ageing factor, without restriction to voltage class.

IEC TR 61857-2:2015(E) gives guidelines to identify the appropriate test method to be used for the evaluation of a proposed Electrical Insulation System (EIS). Some of the standards are for evaluation and classification of the EIS, while other standards identify the appropriate method to evaluate single or multi-factor stresses of a proposed or of an established EIS. This Technical Report is applicable to existing or proposed EIS used in electrotechnical products across a wide range of operating voltages of IEC Standards. The report takes care to select the appropriate standard based on construction and intended operating conditions.

IEC TS 62332-2:2014 is applicable to EIS containing solid and liquid components where the thermal stress is the dominant ageing factor, without restriction to voltage class. This part specifies a sealed tube test procedure for the thermal evaluation and qualification of electrical insulation systems (EIS). One aspect of this procedure is to also provide a method to assign thermal classifications to materials used in EIS where solid and liquid components are both used. This procedure describes a comparative ageing method whereby a reference system composed of kraft paper and mineral oil is compared to a candidate system of any combination of solid and insulating liquid. The test procedures in this part are specifically applicable to liquid immersed transformer insulation systems.

IEC 61858-2:2014 lists the required test procedures for qualification of modifications of an established electrical insulation system (EIS) with respect to its thermal classification. This standard is applicable to EIS used in form-wound electrotechnical devices. The test procedures are comparative in that the performance of a candidate EIS is compared to that of a reference EIS, which has proven service experience in accordance with IEC 60505 or has been evaluated by one of the procedures given in IEC 60085 and IEC 60034-18-31.

IEC 61858-1:2014 lists the required test procedures for qualification of modifications of an established electrical insulation system (EIS) with respect to its thermal classification. This standard is applicable to EIS used in wire-wound winding electrotechnical devices. The test procedures are comparative in that the performance of a candidate EIS is compared to that of a reference EIS, which has proven service experience in accordance with IEC 60505 or has been evaluated by one of the procedures given in the IEC 61857 series. This first edition of IEC 61858-1 cancels and replaces the third edition of IEC 61858, published in 2008. It constitutes a technical and editorial revision. This edition includes the following significant technical changes with respect to the previous edition: a) this part is specifically for wire-wound winding EIS; b) new figures and charts support the contents.

IEC 60505:2011 establishes the basis for estimating the ageing of electrical insulation systems (EIS) under conditions of either electrical, thermal, mechanical, environmental stresses or combinations of these (multifactor stresses). It specifies the principles and procedures that shall be followed, during the development of EIS functional test and evaluation procedures, to establish the estimated service life for a specific EIS. This standard should be used by all IEC technical committees responsible for equipment having an EIS. The contents of the corrigendum of March 2017 have been included in this copy.

IEC/TS 62332-1:2011(E) is applicable to EIS containing solid and liquid components where the thermal stress is the dominant ageing factor, without restriction to voltage class. This part specifies a dual-temperature test procedure for the thermal evaluation and qualification of electrical insulation systems (EIS). The following significant technical changes with respect to the previous edition have been made - Modifications have been made based on an extensive test series conducted using this methodology given in the first edition. This included updating expected times and tempertatures to use in order to obtain useful results, as well as making the range of equipment covered broader. The method can now cover electrotechnical devices using different sealing systems, as well as devices using enamel covered wires.

IEC 61857-21:2009 describes a general-purpose model (GPM) and a tall channel alternative model (GPM-TC) which can be used for the evaluation of wire-wound electrical insulation systems (EIS) where specific electrotechnical products are not available or required. The third edition cancels and replaces the second edition published in 2004, and constitutes editorial revisions to make this standard compatible with Parts 1 and 22.

IEC 61857-1:2008 specifies a general test procedure for the thermal evaluation and qualification of electrical insulation systems (EIS) and establishes a procedure that compares the performance of a candidate EIS to that of a reference EIS. This standard is applicable to existing or proposed EIS used in electrotechnical products with an input voltage of up to 1 000 V where the thermal factor is the dominating ageing factor. This third edition cancels and replaces the second edition published in 2004, and constitutes editorial revisions to make this standard compatible with Parts 21 and 22.

IEC 61857-22:2008 provides a general-purpose procedure for the evaluation of wire-wound systems using a general purpose encapsulated-coil model (ECM) where the application is unknown. This second edition cancels and replaces the first edition published in 2002, and constitutes editorial revisions to make this standard compatible with Parts 1 and 21.

IEC 60085:2007 now distinguishes between thermal classes for electrical insulation systems and electrical insulating materials. It establishes the criteria for evaluating the thermal endurance of either electrical insulating materials (EIM) or electrical insulation systems (EIS). It also establishes the procedure for assigning thermal classes. This standard is applicable where the thermal factor is the dominant ageing factor. The major technical changes with regard to the previous edition concern the fact that this edition is an amalgamation of the third edition of this standard together with IEC 62114:2001.

Applicable to EIS containing solid and liquid components where the thermal stress is the dominant ageing factor, without restriction to voltage class. This procedure is not applicable to EIS containing enamel-coated conductors. This part specifies a dual-temperature test procedure for the thermal evaluation and qualification of electrical insulation systems (EIS).

Lists the required test procedures for qualification of modifications of an established electrical insulation system (EIS) with respect to its thermal classification. This standard is applicable to EIS used in wire-wound electrotechnical devices. The test procedures are comparative in that the performance of a candidate EIS is compared to that of a reference EIS, which has proven service experience in accordance with IEC 60791 or has been evaluated by one of the procedures given in the IEC 61857 series. This second edition cancels and replaces the first edition, published in 1999, and constitutes a technical revision that incorporates test procedures referenced in IEC 60034-18-22.

Specifies a general test procedure for the thermal evaluation and qualification of electrical insulation systems (EIS) and establishes a procedure that compares the performance of a candidate EIS to that of a reference EIS. This basic standard is applicable to existing or proposed EIS used in electrotechnical products with an input voltage of up to 1 000 V where the thermal factor is the dominating ageing factor. This second edition cancels and replaces the first edition published in 1998, and constitutes a technical revision to make this basic standard compatible with parts 21 and 22.

Establishes the basis for estimating the ageing of electrical insulation systems (EIS) under conditions of either electrical, thermal, mechanical, environmental stresses or combinations of these (multifactor stresses). It specifies the principles and procedures that should be followed, during the development of EIS functional test and evaluation procedures, to establish the estimated service life for a specific EIS. The main changes with respect to the previous edition concern the amalgamation of the following standards, which, with the exception of IEC 60727-1, will be withdrawn when this third edition is published: IEC 60791:1984, Performance evaluation of insulation systems based on experience and functional tests IEC 60792-1:1985, The multi-factor functional testing of electrical insulation systems - Part 1: Test procedures IEC 60941:1988, Mechanical endurance functional tests for electrical insulation systems IEC 61356:1995, Functional evaluation of electrical systems - Principles for test procedures when comparative testing is not feasible IEC 61359:1995, Evaluation and identification of electric insulation systems - Environment evaluation IEC 60727-1: 1982, Evaluation of electrical endurance of electrical insulation systems - Part 1: General considerations and evaluation procedures based on normal distributions Elements of IEC 60727-1 that are not amalgamated will be considered in the next edition of that standard.

Describes a general-purpose model (GPM) and a tall channel alternative model (GPM-TC) which can be used for the evaluation of wire-wound EIS where specific electrotechnical products are not available or required. This edition constitutes a technical revision by merging Part 23 into Part 21.

Gives guidance on the application of international standards in assigning a thermal class to electrical insulating materials (EIM) or simple combinations of such materials (IEC 60216-1), to electrical insulation systems (IEC 62114) and to insulation for electrical devices. This new edition distinguishes between thermal classes for electrical insulation systems and electrical insulating materials.

Specifies an encapsulated-coil model (ECM) that can be used for the evaluation of encapsulated wire-wound EIS.

Lists the required test procedures for qualification of modifications of an established electrical insulation system (EIS) with respect to its thermal classification. Applicable to EIS used in wire-wound electrotechnical devices with input voltage up to 1000 V. The test procedures are comparative in that the performance of a candidate EIS is compared to that of a reference EIS, which has proven service experience in accordance with IEC 60791 or has been evaluated by one of the procedures given in IEC 61857 series.

This general purpose model (GPM) can be used for the evaluation of wire-wound electrical insulation systems where specific electrotechnical products are not available or required.

Specifies a general test procedure for the thermal evaluation and qualification of electrical insulation systems (EIS) and establishes a procedure that compares the performance of a candidate EIS to that of a reference EIS. Is applicable to existing or proposed EISs used in electrotechnical products with an input voltage of up to 1 000 V where the thermal factor is the dominating ageing factor.

Applies to electrical insulation systems, specifies a short-time thermal and electrical evaluation procedure - applicable for devices with a supply voltage up to 1000 V (d.c./a.c./pulse), - using a wire-wound coil model; this model may be used for wire-wound applications, such as transformers, chokes, ballasts, reactors, ferrite converters, etc., - with minimum test life of 1500 h at the lowest ageing temperature, - for products that are not normally subjected to vibration. The model shall contain all components of the final product in order to determine chemical interaction under thermal ageing conditions. No modifications are allowed because this ageing program is designed to evaluate the entire EIS.

IEC 61858:2008 lists the required test procedures for qualification of modifications of an established electrical insulation system (EIS) with respect to its thermal classification. This standard is applicable to EIS used in wire-wound electrotechnical devices. The test procedures are comparative in that the performance of a candidate EIS is compared to that of a reference EIS, which has proven service experience in accordance with IEC 60505 or has been evaluated by one of the procedures given in the IEC 61857 series. This third edition cancels and replaces the second edition, published in 2004 by IEC TC 98: Electrical insulation systems (EIS). It constitutes an editorial revision.

Specifies a general-purpose, tall-channel model (GPM-TC) which can be used for the evaluation of wire-wound electrical insulation systems (EIS) where the general-purpose model (GPM) defined in IEC 61857-21 does not offer sufficient space for the electrical insulating materials (EIM) and/or winding wire to be evaluated.

Establishes the thermal classification of an electrical insulation system (EIS). It also identifies recognized procedures for the thermal evaluation of EIS. This standard is applicable to EIS used in electrotechnical devices where the thermal factor is the dominating ageing factor.